In its periodic report on Iran's nuclear program, the United Nation's nuclear watchdog said it found traces of uranium enriched to a level higher than it had previously reported.

NPR's Mike Shuster filed this report for our Newscast unit:

"When International Atomic Energy Agency monitors carry out routine inspections of Iran's nuclear facilities, they take environmental samples to help them determine the nature of uranium enrichment underway.

"It is well know that Iran has manufactured thousands of pounds of 3.5 percent low-enriched uranium, and hundreds of pounds of 20 percent low-enriched uranium.

"The IAEA found these particles at the Fordow enrichment facility, which is the plant buried in a mountain side not far from the city of Qom.

"The agency asked for an explanation, and earlier this month, Iran said that technical reasons beyond the control of those who run the plant were responsible.

"The agency has asked for more details."

This development comes a day after world powers agreed to continued negotiations with Iran over its nuclear program next month in Moscow. Iran has maintained that its nuclear program is for peaceful purposes. But the country has come under increased pressure from U.S. and other world powers because they want Iran to open up its nuclear programs for inspection and to give up any effort it may have to enrich uranium to anything near weapons-grade.